Do you have a Flat Roof?

If you’ve recently moved into a property that features a flat roof, you may not know much about the maintenance of such a roof. Traditionally, domestic flat roofs use two or more built up layers of bituminous felt to act as the weather proofing. It is popular now to see liquid applied systems such as glass fibre which were introduced and now widely used.

Single Ply membranes are also still used and are particularly suited for larger roofs. Bitumen membranes are still the most used system for flat roofing needs and are of much higher quality than those used in previous decades. They are now known as Reinforced

Bitumen Membranes (RBM). Mastic asphalt is sometimes used but, because of its weight, it has to have a much stronger roof construction.

The construction of the roof deck and ceiling has an important effect on the behaviour of the waterproofing material on top. There are two technical terms used in the building industry that relate to flat roofing and they are Warm Roof and Cold Roof. Having a warm roof construction is highly recommended in the UK. For Evesham Flat Roofing, visit http://www.lwroofing.co.uk/

Warm Roof –

This type of construction has the insulation above the roof deck, thus keeping the deck ‘Warm’. This is usually the most satisfactory construction for domestic properties as it avoids the need for ventilation of the roof structure. The membrane is then attached to the insulation.

Cold Roof –

Many domestic flat roofs have the waterproofing laid directly onto the deck, and any insulation placed above the ceiling. This arrangement allows the deck to become ‘Cold’.

In cold weather, such roofs are very prone to condensation, which can cause materials to decay and distort. To reduce this risk, through-ventilation must be provided to every single space above the insulation but this is often difficult to achieve, for example if the roof abuts the wall of a house. If you have an existing cold roof in need of refurbishment, it should be converted to a warm roof.

More info about Flat Roofing

• With a flat roof, the waterproofing is always supported by a structural roof deck. This is usually made up of timber boarding supported on joists. The ceiling, if any, is usually fixed directly to the underside of the joists.
• Garages may be un-insulated, but most roofs above the lived-in part of the house will be insulated to comply with Building Regulations. In houses, the insulation is sometimes placed immediately above the ceiling.
• Some specialised insulations can also be placed above the waterproofing, but this sort of construction is normally confined to commercial and industrial buildings and has very seldom been used on domestic buildings.
• In almost all cases where RBM has been installed, the surface of the waterproofing will need protection, both from ultraviolet light and from fire from external sources.
• The Building Regulations lay down the degree of protection required in the case of fire. This can be achieved by adding a layer of mineral chippings bedded

in compound to the surface of the roof.